Process for producing an organic photosensitive material preventing brushing

Abstract: A process for producing an organic photosensitive material preventing brushing by applying an organic photosensitive material dispersed or dissolved in an organic solvent onto the surface of a blank tube consisting of an electrically conducting substrate such as aluminium, wherein when the thickness of the blank tube is t (cm) and the thickness of the photosensitive material layer is d (cm), the thickness of said photosensitive material layer being set so as to satisfy the equation: d= kt wherein k is 0.13 or less. Brushing can be effectively prevented by controlling only the thickness of the blank tube upon which the photosensitive layer is formed and the thickness of the photosensitive layer.

Description: Background of the Invention The present invention relates to a process for producing a single layer type organic photosensitive material preventing brushing. At present, organic photosensitive materials (OPCs) have been extensively used as photosensitive materials for the electrostatic photographic devices. The organic photosensitive materials can be roughly divided into those of the single-layer type in which a single layer obtained by dispersing a charge-generating material (CGM) and a charge-transporting material (CTM) in a binder resin, is formed on a blank tube such as of aluminium, and those in which a layer containing CGM and a layer containing CTM are laminated on a blank tube (usually, the CGM is contained in the lower layer). These organic photosensitive materials are obtained by preparing a coating solution by dissolving or dispersing the CGM and/or the CTM and a binder resin in an organic solvent, applying the coating solution onto the blank tube by using a blade or by immersion, and drying the coating solution. Generally, however, the coating solution containing CGM contains an organic solvent in large amounts. Due to the latent heat at the time when the solvent vaporizes after it is applied, therefore, the temperature drops on the surface of the film causing the brushing (whitening) to take place easily. In the case of the organic photosensitive material of the laminated type, the problem is not so serious since the CTM layer is formed on the CGM layer. In the case of the single-layer type organic photosensitive material, however, the brushing takes place on the surface of the photosensitive material and the surface becomes rugged. Therefore, the photosensitive material loses properties such as repetition property when used continuously, resistance against ozone and like properties. The production of electrophotographic materials by various means is disclosed in for example JP-A-60/254,141, JP-A-2/203,348, JP-A-57/167,031, EP-A-0,406,001, US-A-5,120,627, US-A-4,693,453, EP-A-0,082,011 and EP-A-0,093,331. Summary of the Invention The present invention therefore seeks to provide a process for producing an organic photosensitive material which effectively prevents brushing. According to the present invention, there is provided a process for producing an organic photosensitive material having a single photosensitive layer on an electrically conducting substrate wherein brushing is prevented by applying an organic photosensitive material dissolved or dispersed in an organic solution onto the surface of the electrically conducting substrate under conditions wherein: when the thickness of the electrically conducting substrate is t (cm) and the thickness of the photosensitive material layer is d (cm), the thickness of the photosensitive material layer is such that equation (1) is satisfied: d= kt wherein k is a coefficient expressed by equation (2); k ≤ ΔT.C sub . d sub /H solv .d solv . ((1/C)-1) wherein C is the proportion by weight of solid components in the solution or dispersion and is from 0.25 to 0.35, C sub is the specific heat (cal/g.deg)* of the electrically conducting substrate, d sub is the density (g/cm 3 ) of the electrically conducting substrate, H solv is the vaporisation enthalpy (cal/g) of the organic solvent, d solv is the specific gravity (g/cm 3 ) of the organic solvent, and ΔT is the maximum temperature drop that does not cause dew condensation during vaporisation of the organic solvent following application of the solution or dispersion of the organic photosensitive material in the organic solvent. Brief Description of the Drawings Fig. 1 is a diagram illustrating the regions where no brushing is taking place depending upon the thickness (t) of a blank tube that forms a photosensitive material layer and the thickness (d) of the photosensitive material layer [in an environment of 25°C, humidity 53.8% (ΔT = 10°C); and Fig. 2 is a diagram showing temperature vs. saturation amount of water. Detailed Description of the Invention According to the present invention, a quite distinguished effect is obtained in that brushing is prevented by controlling only the thickness of an electrically conducting substrate that is forming a photosensitive material layer and the thickness of the photosensitive material layer. The present inventors have conducted extensive study concerning a process for producing an organic photosensitive material by applying an organic solvent solution or a dispersion of an organic photosensitive material onto the surface of an electrically conducting substrate such as an aluminium blank tube followed by drying. The inventors have plotted the thicknesses (d; cm) of the photosensitive material layer relative to the thicknesses (t; cm) of the blank tube that forms the photosensitive material layer, and have found a novel fact that there exist iinear brushing boundary lines as shown in Fig. 1 (the straight lines correspond to those shown in Table 1 appearing later, and wherein the straight line 1 is that of when C = 0.5, the straight line 2 is that of when C = 0.3, and the straight line 3 is that of when C = 0.1)(regions under the boundary lines are those regions where no brushing takes place), and that such boundary lines necessarily exist in any material irrespective of the organic photosensitive materials used for forming the photosensitive material layer or the kind of the blank tube that is the electrically conducting substrate, and have thus completed the present invention. The reasons why the brushing is effectively prevented when the conditions of the above equation (1) are satisfied in the process of the present invention, are attributed as described below. Here, described below is the case where the blank tube is used as the electrically conducting substrate. The following equation represents the temperature drop on the surface of the blank tube that takes place when an organic solvent solution or dispersion of an organic photosensitive material (hereinafter often referred to simply as coating solution) is applied onto the blank tube or aluminium or the like to form a film. Here, the film thickness of the solvent can be substituted by the film thickness of the photosensitive layer (thickness of photosensitive layer after dried) x [(1/concentration of solid components) - 1]. Therefore, if the thickness of the photosensitive layer is denoted by d (cm) and the thickness of the blank tube by t (cm), the temperature drop ΔT 1 on the surface of the blank tube is given by the following equation (3): ΔT 1 =d·[(1/C)-1]·d SOLV ·H SOLV /t·C SUB ·d SUB where C is a concentration (weight percentage) of solid components in said solution or said dispersion, d SOLV is a specific gravity (g/cm 3 ) of the organic solvent, H SOLV is a vaporization enthalpy (cal/g)* of the organic solvent, C SUB is a specific heat (cal/g deg) of the blank tube and d SUB is a density (g/cm 3 ) of the blank tube. In order to prevent the brushing, furthermore, the temperature drop on the surface of the blank tube must be suppressed during the vaporization of the organic solvent. That is, as the temperature drop increases, the water vapor pressure is saturated under the coating environment and the moisture in the air forms dew resulting in the occurrence of brushing. This, on the other hand, means that the temperature drop is allowable if it is within a range in which the water vapor pressure is smaller than the saturation water vapor pressure in the coating environment. Fig. 2 shows a curve (humidity 100%) on which the saturation amount of water is plotted relative to the temperatures, wherein the hatched portion over the saturation amount of water is the region where the brushing takes place. For instance, if the coating is carried out in an environment of 25°C (saturation amount of water at this temperature is 23.756 g) and a humidity of 50%, the amount of water at 25°C and a humidity of 50% is calculated to be 11.88 g since, Humidity (%) = (Amount of water present/Saturation amount of water at that temperature) x 100. This working environment is represented by a point P in Fig. 2. Therefore, the temperature at which the amount of water of 11.88 g becomes a saturation amount of water is about 14°C from Fig. 2. It will be therefore understood that the allowable temperature drop in this case is 11°C. As will be obvious from the above description, when the allowable temperature drop is ΔT (°C), the brushing can be prevented under the condition where ΔT ≧ ΔT 1 . When the above equation (3) is taken into consideration, therefore, the above condition is expressed as ΔT ≧ d·[(1/C) - 1]·d SOLV ·H SOLV /t·C SUB ·d SUB which can, then, be rewritten to derive the following equation (4), d ≦ {ΔT·C SUB ·d SUB /H SOLV ·d SOLV ·[(1/C) - 1]}·t Therefore, if ΔT·C SUB ·d SUB /H SOLV ·d SOLV ·[(1/C) - 1] = k 1 then the condition given by the following equation (5), d ≦ k 1 t is the one for preventing the brushing. According to the above equation, therefore, when the thickness (d) of the photosensitive layer is plotted relative to the thickness (t) of the blank tube, there exists a boundary line of a primary function that defines a region where the brushing does not take place irrespective of what kind of photosensitive material is used. Therefore, k ≦ k 1 is set, i.e., the coefficient k is set that satisfies the above-mentioned equation (2), and the photosensitive layer is formed while setting the thickness (t) of the blank tube and the thickness (d) of the photosensitive layer in compliance with the equation (1), thereby to effectively prevent the occurrence of brushing. According to the present invention, it is desired that the above coefficient k is usually set to be 0.13 or smaller. That is, k 1 (that defines the upper limit value of coefficient k) in the above equation (5) is a value determined by the concentration of solid component in the coating solution, kind of solvent, kind of blank tube and conditions in the coating environment. If the conditions which are usually employed are taken into consideration, the coefficient k is set to lie within the above-mentioned range in order to satisfy the conditions represented by the above equation (2). Electrically conducting substrate According to the present invention, the electrically conducting substrate used for forming the photosensitive layer may be of a tubular shape (blank tube) or a plate shape, and may be made of any single metal such as aluminium, an aluminium alloy, steel, tin, platinum, gold, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, a stainless steel, brass or the like. Coating solution As a coating solution to be applied onto the surface of the above substrate, there is used a solution that is obtained by dissolving or dispersing a charge-transporting substance and a charge-generating substance in a resin solution. The coating solution is applied and the solvent is then vaporized in order to form a photosensitive layer of the type of single dispersion layer. Examples of the charge-transporting substance include fluorenone-type compounds such as chloranil, tetracyanoethylene, 2,4,7-trinitro-9-fluorenone, and the like; nitro compounds such as 2,4,8-trinitrothioxanthone, dinitroanthracene and the like; hydrazone-type compounds such as N,N-diethylaminobenzaldehyde, N,N-diphenylhydrazone, N-methyl-3-carbazolylaldehyde, and the like; oxadiazole-type compounds such as 2,5-di(4-dimethylaminophenyl)-1,3,4-oxadiazole and the like; styryl-type compounds such as 9-(4-diethylaminostyryl) anthracene and the like; carbazole-type compounds such as N-ethylcarbazole and the like; pyrazoline-type compounds such as 1-phenyl-3-(p-dimelhylaminophenyl)pyrazoline and the like; oxazole-type compounds such as 2-(p-diethylaminophenyl)-4-(p-dimethylaminophenyl)-5-(2-chlorophenyl) oxazole and the like; isooxazole-type compounds; thiazole-type compounds such as 2-(p-diethylaminostyryl)-6-diethylaminobenzothiazole and the like; amine derivatives such as triphenylamine, 4,4'-bis[N-(3-methylphenyl)-N-phenylamino] diphenyl and the like; nitrogen-containing cyclic compounds such as stilbene-type compound, thiadiazole-type compound, imidazole-type compound, pyrazole-type compound, indole-type compound, triazole-type compound and like compounds; condensed polycyclic compounds; succinic anhydride; maleic anhydride; dibromomaleic anhydride; polyvinyl pyrene; polyvinyl anthracene; ethylcarbazole formaldehyde resin, and the like, which may be used in a single kind or in a combination of two or more kinds. The photoconducting polymer such as a poly-N-vinyl carbazoie or the like may be used as a binder resin that will be described later. Examples of the charge-generating substance include a variety of materials that have been known so far, such as pyrylium salt, azo-type compound, dis-azo-type compound, tris-azo-type compound, anthanthrone-type compound, phthalocyanine-type compound, indigo-type compound, triphenylmethane-type compound, threne-type compound, toluidine-type compound, pyrazoline-type compound, perylene-type compound and quinacridone-type compound, which may be used in a single kind or in a combination of two or more kinds. Examples of the resin that serves as a binder include such polymers as styrene-type polymer, styrenebutadiene copolymer, styrene-acrylonitrile copolymer, stylene-maleic acid copolymer, acrylic polymer, styrene-acrylic polymer, ethylene-vinyl acetate copolymer, polyester, alkid resin, polyamide, polyurethane, epoxy resin, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, silicone resin, ketone resin, polyvinylbutyral resin, polyether resin, phenol resin, as well as photo-curing resins such as epoxy acrylate, urethane acrylate and the like, which may be used in a single kind or in a combination of two or more kinds. Any suitable organic solvent can be used for dissolving or dispersing the above-mentioned charge-transporting substance, charge-generating substance and resin. Generally, however, an organic solvent having a relatively small vaporization enthalpy is used, such as tetrahydrofurane (THF), toluene, dichloromethane, trichloroethane, or the like. The coating solution may be further blended with any widely known sensitizers such as halonaphthoquinones, acenaphthylenes and the like, as well as various additives such as plasticizers, ultraviolet ray-absorbing agents, antioxidants and the like, thereby to form a photosensitive layer containing these additives. The above-mentioned coating solution usually contains the charge-transporting substance in an amount of 30 to 120 parts by weight and, particularly, 50 to 100 parts by weight and contains the charge-generating substance in an amount of 0.5 to 20 parts by weight and, particularly, 1 to 5 parts by weight per 100 parts by weight of the above-mentioned resin. Furthermore, the organic solvent is used in such an amount that the proportion by weight (C) of the solid component is 0.25 to 0.35. When the proportion by weight of the solid component is lower than the above range, the coating solution drips. When the proportion by weight of the solid component is higher than the above range, on the other hand, it becomes difficult to adjust the amount of coating. Preparation of organic photosensitive material According to the present invention, the above-mentioned coating solution is applied onto the electrically conducting blank tube or the plate by a widely known means with the exception of setting the photosensitive layer to have a thickness that satisfies the conditions of the aforementioned equation (1) and, then, the organic solvent is removed to obtain an organic photosensitive material of the type of single layer dispersion. In this case, the thickness of the photosensitive layer that is formed can be easily adjusted by adjusting the rate of coating depending upon the weight percentage of solid components in the coating solution. In applying the coating solution, furthermore, it is desired to so set the conditions of coating environment (i.e., temperature and humidity) that the allowable temperature drop ΔT is 5°C or larger and, particularly, from 5 to 20°C. When the coating solution is applied under the conditions of environment in which the allowable temperature drop ΔT is smaller than 5°C, the temperature drop due to the vaporization of the solvent may exceed the allowable temperature drop making it difficult to so adjust the thickness of the photosensitive layer as to satisfy the aforementioned equation (1). The photosensitive layer usually has a thickness of 15 µm or larger so that it exhibits its functions to a sufficient degree. Adjusting the thickness of the photosensitive layer so as to satisfy the aforementioned equation (1) means that the amount of solvent to be removed by vaporization has been determined. Therefore, if the aforementioned equation (1) is satisfied, the temperature drop inevitably becomes smaller than the allowable temperature drop ΔT. As described above, the present invention makes it possible to produce an organic photosensitive material while effectively suppressing the occurrence of brushing. Example 1 The following three conditions were set as a coating environment: (i) Temperature: 25°C, humidity: 28.6%, allowable temperature drop ΔT: 20° C, (ii) Temperature: 25°C, humidity: 53.8%, allowable temperature drop ΔT: 10° C, (iii) Temperature: 25°C, humidity: 73.8%, allowable temperature drop ΔT: 5°C. The allowable temperature drops ΔT in the environmental conditions were found from Fig. 2. Furthermore, an N,N,N',N'-tetrakis(3-metyipenyl)-1,3-diaminobenzene was used as the charge-transporting substance, a metal-free phthalocyanine was used as the charge-generating substance, and THF (vaporization enthalpy: 486.0 J/g (116.1 cal/g), specific gravity: 0.88 g/cm 3 ) was used as the organic solvent to prepare coating solutions having weight percentages (C) of solid components shown in Table 1. Here, in forming the photosensitive layers by applying the above-mentioned coating solutions to the aluminum blank tube (thickness: 1.5 cm, specific heat: 0.9615 J/g·deg (0.2297 cal/g·deg), density: 2.6989 g/cm 3 ) under the above-mentioned environmental conditions, the conditions of the equation (5) for preventing the brushing were shown in Table 1 below relying upon the coefficient k 1 calculated from the following equation, k 1 = ΔT·C SUB ·d SUB /H SOLV ·d SOLV ·((1/C) -1) Weight percentage C of solid component in coating solution Conditions in coating environment (i) ΔT:20° C (ii) ΔT:10° C (iii) ΔT:5° C 0.1 d ≦ 0.013484t d ≦ 0.006742t d ≦ 0.003371t 0.3 d ≦ 0.052010t d ≦ 0.026005t d ≦ 0.013002t 0.5 d ≦ 0.121356t d ≦ 0.060678t d ≦ 0.030339t Brushing has developed in none of the organic photosensitive materials that were prepared under the aforementioned environmental conditions by setting the thickness of the photosensitive layer in compliance with the equation (1) by using a coefficient k which is smaller than k 1 that is shown in Table 1. Brushing, on the other hand, has developed in all of the organic photosensitive materials that were prepared in the same manner but using a coefficient k larger than k 1 . Example 2 A temperature of 25°C and a humidity of 50% were employed as conditions of the coating environment (allowable temperature drop ΔT: 11° C), and the coating solution of Example 1 haying a weight percentage of solid components of 0.3 was applied onto the aluminum blank tube to form a photosensitive layer that was 20 µm thick. In this case, the coefficient k 1 calculated in compliance with the above formula was 0.0286. Therefore, the condition of the equation (5) for preventing the brushing was 0.002 ≦ 0.0286t, i.e., t ≧ 0.07 (cm), where t is the thickness of the aluminum blank tube. Aluminum blank tubes of various thicknesses were used to form photosensitive layers of a thickness of 20 µm based upon the above conditional equation. It was found that the brushing did not develop when there were used aluminum blank tubes having thicknesses of 0.07 cm or larger.

Claims: A process for producing an organic photosensitive material having a single photosensitive layer on an electrically conducting substrate wherein brushing is prevented by applying an organic photosensitive material dissolved or dispersed in an organic solution onto the surface of the electrically conducting substrate under conditions wherein: when the thickness of the electrically conducting substrate is t (cm) and the thickness of the photosensitive material layer is d (cm), the thickness of the photosensitive material layer is such that equation (1) is satisfied: d= kt wherein k is a coefficient expressed by equation (2); k ≤ ΔT.C sub . d sub /H solv .d solv . ((1/C)-1) wherein C is the proportion by weight of solid components in the solution or dispersion and is from 0.25 to 0.35, C sub is the specific heat (cal/g.deg)* of the electrically conducting substrate, d sub is the density (g/cm 3 ) of the electrically conducting substrate, H solv is the vaporisation enthalpy (cal/g) of the organic solvent, d solv is the specific gravity (g/cm 3 ) of the organic solvent, and ΔT is the maximum temperature drop that does not cause dew condensation during vaporisation of the organic solvent following application of the solution or dispersion of the organic photosensitive material in the organic solvent. A process according to claim 1, wherein the coefficient (K) is 0.13 or smaller less. A process according to claim 1 or 2 wherein the temperature drop (ΔT) is from 5 to 20°C.

Inventors: KATSUKAWA MASATO, TANAKA MASASHI, KATSUKAWA, MASATO, TANAKA, MASASHI, KATSUKAWA, MASATO, C/O MITA INDUSTRIAL CO., LTD., TANAKA, MASASHI, C/O MITA INDUSTRIAL CO., LTD.
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: G03G5
IPC codes: G03G5